Apparatus for loaded-telephone-line system.



T. SHAW & w. FONDILLER.

APPARATUS FOR LOADED TELEPHONE LINE SYSTEMS.

APPLICATION FILED SEPT-12.1914.

Patented Dec. 31, 1918. 3m

W/Meases THQMAS. SHA'W, AQ ENW J LW S X.. 1-' D F rm lator m roan, n rnassmnpps, 13y assrenmnnrsmo WESTERN ELECTRIC- com PANY, INCORPORATED, A CORPORATION OF NEW YORK.

arrannrus roe nofiiiii'n-rnnni nonniinns rs'riiiiis.

siitiifitasit of Letters retest.

Patented D c.- 31, 191a.

Application filed Se tember 12. 1914. Serial m. 861,421.

To all whoin it. may concern:

Be it known that we, THoMAs SHAW aiid have invented certain new and usefulllhv provements in Apparatus for Loaded-Telephone-Line Systems, of which the following is a full, clear. tion.

This invention relates to loaded telephone lines, and more particularly to loaded phantom line systems; Itsobject is the mainteuance of constant or nearly constant characteristics of the line conductors under varying conditions met in practice, whereby the circuits are rendered suitable for the ap plication thereto of amplifying repeaters and more satisfactory for superimposed telegraph working.

Difliculty has been experienced heretofore .inthe application of amlplify'ing repeaters to loaded lines, particular y in hantom systems using-open-wire lines. wing to the exposure of the line conductors to lightning or other, source of strong foreign currents, the loading coils availab e were subject to considerable changes in inductance to telephonic curren'ts, resulting in singing of the repeaters. Another difficulty arose from transient changes in the resistance of the loading coils when telegraph currents were superposed upon the telephone currents, this resulting in serious impalrment to telephonlc transmission.

In long distance telephony it is a desirable practice to divide the-line between distant stations into two or more sections and to provide at each point of division an amplifying system preferably comprising two amplifiers, one for repeating in each direction. To render such a sectional line suitable for the amplifiers, an artificial line or balancing net-work, as it is sometimes called, is connected to the terminus of each section at each such point, the purpose of the artificial line being to neutralize the section to which it is joined to currents tending to cause singing of the amplifying apparatus. The ar-' tificial line itself is maintained constant as to its electrical characteristics since 1t Is not concise, and exact descripsubject to outside disturbances, and the/in troduction'of loading coils in the external line sections has been unsatisfactory in such systems because .transient changes in the characteristics of the loading coils in these sections is not or cannot be offset by corresponding changes in the artificial lineseetlons without frequent adjustment of the artificial line.

It has been found that the changes in inductance referred to are caused by excessive so I residual magnetism in the cores of the load- 1 ing coils, which varies from time to time and variably reduces or changes the winding inductances to very small magnetizing forces, such as those produced by telephonic currents. The result in general is a continual variation or irregularity which has imposed a serious limitation in the application of amplifying repeaters and telegraph instruments to loaded lines. For successful rcpeater or simultaneous telegraph working, it is necessary to maintain constant or nearly constant line characteristics,

Furthermore, in loaded phantom systems it is necessary that there be a close electromagnetic, as well as electrostatic balance in the loading coils, as provided for in accordance with the Campbell &- Shaw- Patent No. 980,921. Such a balance is not possible with loading coils made as described in Pupin Patents Nos. 652,230 and 652,231, not only becausev their windings are not properly distributed to obtain the balance necessary in phantom circuits, but also because anairgap in the core, as indicated in the Pupin patents, even if the windings are distributed on the core in accordance with the Campbell & Shaw patent, would produce an unbalanced condition resulting in serious crosstalk between the circuits. The purpose of the gap in the Pupin coil is, as stated in the Pupin patent, solely to reduce the permeability of the magnetic circuit and so to keep down the magnetization and the accompanying coil, may be provided in accordance with.

this invention with a plurality of air-gaps uniformly distributed about the core. Furthermore, although there is a slight increase in the ohmic resistance of the winding conductors, due to the air-gaps, there is, to offset this, a diminution of the effective resistance due to a reduction in hysteresis and eddy current losses in the core. the air-gap coils constructed in accordance with this invention give a very large net gain in line efficiency by permitting the use of repeaters adjusted to a very high degree of amplification, and by permitting more satisfactory telephonic transmission under the condition'of superposed telegraph work- I I a A type of phantom circuit loading coil,

- to which the invention hasbeen applied,

consists of eight winding grouped upon a toroidal core. The core is dividedby winding separators into four quarter sections or quadrants, and each quadrant has an inner and an outer winding. The inner winding of one quadrant is connected to the outer winding of the opposite quadrant, and these two windings together form a ingle line winding, that is to say, one which is included in a single line conductor of the system. The side circuit loading coil preferably used in the system of the invention, consists of four windings grouped upon a toroidal iron wire core. the winding space being divided into two semi-circular sections, and the inner winding of one section being connected in series with the outer winding of the other section. The two sectional windings of the side circuitcoil thus paired form together a single line winding of the system. The air-gaps introduced into the core of the phantom coil, in accordance with this invention, may separate the core into four quarter sections, corresponding to the four winding sections, although it is within the scope of this invention to employ a larger number than four or less than four, say two, likewise uniformly distributed around the core. Two air-gaps have actually been found suflicient and preferable under certain conditions for the phantom coil, and are also the preferred number for the side circuit coil.

Under all conditions, however, itis important that the gaps shall be symmetrically located with respect to the plurality of windings which 0 to make up the line windings of the c011. I

More than this.

The invention will be more fully understood by reference to the accompanying drawing, wherein Figure 1 illustrates diagrammatically a phantom telephone line system employing air-gap loading coils and amplifying re- W 3 v Fig. 2 illustrates the core cutting step in the process of manufacture; and

Fig. 3 is a cross-section of a loading coil taken along the center line of its core.

Referring to Fig. 1, four line conductors 1, 2, 3, 4 are arranged to provide three circuits, one a side circuit of conductors 1 and 2 extending between telephone stations 5 and 6; another also a side circuit of conductors 3 and 4 extending between stations 7 and 8, and a third or phantom circuit of conductors 1, 2 and 3, 4 extending between stations 9 and 10.

The circuit of conductors 1, 2 is provided with side circuit loading coils 11 and'12, and an amplifying system comprising repeaters 13 and 14. The circuit of conductors- 3 and a is likewise provided with side circuit loading coils 15 and 16, and an amplifying system comprising repeaters 17 and 18. The phantom circuit 13 provided with phantom loading coils 19 and 20 and an amplifying system comprising repeaters 21 and 22. Each of the phantom loading coils, 19 for example, is provided with a core 23, withav plurality of air-gaps 24, and eight windings 26 to 33 inclusive distributed around the core in quarter sections or quad-' rants, with the outer winding, ay 26, of one quadrant being in series with the inner wmding 32 of the opposite ,qua-drantQ The air-gaps 24 are uniformly distributed around the core. As shown, they may separate the core into four quadrants corresponding to then placed on the core leaving spaces between the sections for the cutting operation, which 13 performed in any desired manner, for example, by a band-saw41 as shown in Fig. 2. After the coil is thus separated into sections, sheets of insulating material 42 are inserted n pla e of the gaps. The whole is then he]. together by clamps 44, 4:5 as shown in Fig. These clamps may be of German I silver or some other non-magnetic material having high resistance or insulating chareta-easel acteristics so as toavoidlosses therein due to tray magnetic fields from the coil Wind- The principal function of the air-gaps, when used in loading coils, is to insure that the electrical constants of the coil for telephone conditions will not be materially altered by any degree of magnetization that maj be superposed on the corealong with the small forces due to the telephone currents themselves. The air-gaps impart to the magnetic circuit not only resistance to magnetization but also the property of selfdemagnetization, in consequence of which the removal of the residual magnetism. is accomplished when the superposed magnetic force is withdrawn.

These efiects depend on the proportion of the air-gaps to the iron circuit, and are greater as the length of the gap is increased. Since an increase in the demagnetization factor results also in a reduction of the effective permeability of the core, and consequently in an increase of the amount of copper necessary to give the same inductance as well as an increase in the size and cost of the iron case, the best length of the gaps will be that which just gives a sutiicient demagnetizing effect to insure that under any con ditions of superposed magnetization that may arise in practice, the electrical const-ants of the coil will not vary more than an amount known not to be harmful.

If the air-gap is too small the demagnetiz ing effect will be insufficient to secure the required onstancy, and if too great a large and unwieldlycoil and case results in which a great sacrifice of efliciency has been made with no valuable gain in constancy.

It has been found that there is a saturation value of the residual magnetism of a closed circuit core, which is reached upon the application of magnetic force suiiicienl to magnetize the core to a point just above the knee of the curve of induced magnetism. and that any further increase in the magnetizing force will not substantially increase the residual magnetism.

l or a core having air-gaps there exists a similar saturation value of the residual magnetism, but on account of the self-demagnetizing properties of the circuit this value is always smaller than for the closed core, and by 'varying the proportions of the gaps may he reduced to any desired extent. The maximum residual magnetization that can exist in a magnetic circuit having air-gaps may be determined from the hysteresis, or, as it is generally termed, the B-'-H, loop for the material itself, pro 'ided that in thedetermiuation of the loop the magnetic force has been raised sufficiently to insure that the residual magnetization reaches its saturation value.

The rc'lationsliipbetween the proportions of the air-gaps and their demagnctizing efiect is shown by the equation AL B-= L(1 in which air-gaps A =clross-section of path in iron' The term nAL E" in which tliecoeflicientof B for a giveneore having small gaps suitable for the purposes of this invention is substantially proportional to the length of the gap, represents a magnetic force ofoppositc sense to the applied force tending to demagnetize the iron or to prevent its attaining to the full magnetization unde' any given force.

The proper proportions of-thc air-gap in each case are best determined directly by ex periment. This may be done by observing for various lengths of gap the total range of change of the e-fi'ective permeability of the whole magnetic cirzuit to the small forces due to the telephone currents after the coil has been subjected to various cycles of strong magnetization, such as may be met with in practice. The proper air-gap .will be chosen from these observations as that for which the total variation does not exceed the limiting value, say 5%, imposed by the working requirements of the telephone line. A similar method may be followed to determine the most suitable gap to use in cases where the variation of the effective resistance of the coils is the limiting requirement, such as the case of simultaneous use of the/line conductors for telephoning and telegraphmgd The amplifying repeaters referred to may be of the audion type, each. for example 13,- comprising a cathode in theform of a heated filament 46, an output electrode or plate l7, and an input electrode or grid 48. The filament is heated by a battery 49. Abattery ,50 is provided in the output circuit, which includes also the primary winding 5.1 of an output repeating coil; A battery 52 is included in the input circuit, which also includesthe secondary winding 53 of an input repeating coil. Tli 'scondary windings (it of the output repeating coil are included serially in a part of the circuit system of conductors 1 and 2, this part being electrically balanced at the amplifying apparatus by a line network 55. The primary wind= ings 56 of the input repeating coil are bridged across the other part of the circuit system of conductors 1, 2, and this other part is likewise balanced by a line network 57.

The repeater 13 is adapted to repeat telephonic currents transmitted from station 5 to station 6. In the same manner the repeater 14 is adapted to repeat from station 6 to 5. It will be noted that the phantom circuit, through the amplifying system includin the audions 21, 22, is completed by way 0 conductors 58, 59, 60 and 61 tapped from the middle points of the windings 56 of the other two circuits. I

Although only one set of amplifiers and two sets of loadlng coils are shown for each circuit, it is to be understood that a greater number of each may be and ordinarily would be used in practice.

Whenever the loading coils are invaded by strong foreign currents, the demagnetizing poles, due to the plural air-gaps, may be relied upon to maintain the line characteristics ractically constant and a practically perect balance between the several parts of the circuits and their line networks. It is therefore possible to use very powerful repeaters adjusted to their maximum degree of amplification and to give satisfactory telephone service under the severest conditions of siing a plurality of core sections separated by non-magnetic aps, the ratio of total length of ap to total length of core circuit bein suc that under varying degrees of residua magnetism the initial permeability to telephonic currents of the core material will not be materially altered. v 0 4'. A phantom loading coil having a toro1- dal core and four sets of line windings distributed symmetrically upon four core sections, said core. being separated by nonmagnetic gaps into sections corresponding to the winding sections.

5. A phantom loading coil having a toroidal core and inner and outer windings on a plurality of sections thereof, each line conductor through the coil includin the inner and the outer windings respectively of op 0- site core sections, the said core having a p urality of non-magnetic gaps uniformly distributed about the core and equal in number to the winding sections thereof.

6. A loading coil for telephone lines comprising a toroidal core of magnetic material divided into sections, non-magnetic separators between said sections and a clamping device for retaining the said core sections and separators in osition.

7. A loading'coil for telephone lines comprisin a toroidal core of magnetic material divide into sections, non-magnetic separators between said sections and a clamp of non-magnetic metal and having high electrical resistance for holding said core sections and said separators in position.

8. The method of manufacturing loading coils for telephone lines which consists in assembling a toroidal core, placing windings thereon in sections, cutting gaps in said core between the winding sections, placing nonmagnetic separators in place of the gaps and clamping said sections and said separators together.

9. A'loading coil having a core of generally toroidal orm, said core being in circumferential sections separated from one another by symmetrically arranged non-magnetic material.

10. A loading coil having a core of generally toroidal form, said core being in circumferential sections separated from one another by symmetrically arranged nonmagnetic solids. I

11. A loading coil having a core of generally toroidal form, said core being in circumferential sections separated from one another by a non-magnetic solid, windings upon the core, and means surrounding the windings for maintaining the core sections and separating material in position.

12. A loading coil having a core of generally toroidal form, said core being in circumferential sections separated from one another by non-magnetic material, and windings upon the core symmetrically arranged with respect to the sections.

13. A loading coil of generally toroidal form, a magnetic core therefor, a plurality of symmetrically arranged windings on said core, and non-magnetic means between the winding sections to break the continunity of the magnetic circuit.

14. A loading coil of generally toroidal form, a magnetic core therefor. a plurality of symmetrically arranged windings on said core, and a non-magnetic gap in the core located at a junction between two winding.

sections.

15. A loading coil of generally toroidal form, a magnetlc' core therefor comprising a plurality of separate sections. a plurality, of symmetrically arranged windings on said core sections, and non-magnetic material be tween said core sections.

16. A loading coil of generallytoroidal form, a magnetic core therefor comprising a our names this 10th day of September A. D.

- plurality of separate sections, a plurality of 1.914.

symmetrically arranged windings on said I core sections, non-magnetic material between B% said sections, and a clamp of non-magnetic material for holding said windings and; core Witnesses: sections in position. SAMUEL RAcclNsm,

In witness whereof, We hereunto subscribe ROBERT S. SUTLIFFE. 

